1. Technical Field
The present invention relates to a belt-driven centrifuge in which rotation force of a motor is transmitted to a rotor by means of a force transmission member such as a belt.
2. Related Art
A centrifuge rotates a rotor containing a sample for separation in a tube or a bottle at a high speed by a drive unit such as a motor so as to separate and refine the sample contained in the rotor. The rotation speed of the rotor varies depending on the usage of the centrifuge. The centrifuge has a wide range of product line from relatively low speed centrifuges having a maximum rotation speed of several thousand rpm to relatively high speed centrifuges having a maximum rotation speed of 150,000 rpm.
The centrifuge can be classified into a floor install type centrifuge used in a state that the centrifuge is fixed on a floor and a desktop type centrifuge used in a state that the centrifuge is installed on a platform. In the floor install type centrifuge, as shown in FIG. 10, the rotor 1 containing the sample therein is mounted on an output rotation shaft 2a of the motor 2 serving as a driving source so as to transmit the rotation force of the motor 2 directly to the rotor 1 through the output shaft 2a (in a direct-driven manner). Meanwhile, when the desktop type centrifuge is arranged in the same manner (i.e., in the direct-driven manner) as the floor install type centrifuge in order to mount the centrifuge on the platform, the height of the centrifuge increases, thereby making it difficult to use. Therefore, in order to decrease the height of the centrifuge and enhance usability, the present applicant developed a belt-driven centrifuge, as shown in FIG. 11, in which the motor 2 is disposed adjacent to the rotor 1 rather than connecting the rotor 1 directly to the motor 2 and the rotation force of the motor 2 is transmitted to the rotor 1 through a belt 11, thereby driving the centrifuge.
A known belt-driven centrifuge 200 shown in FIG. 11 includes the rotor 1 containing the sample for separation, a rotor rotation shaft 9 mounting the rotor 1 thereon, a rotor pulley 10b fixed to the rotor rotation shaft 9, a motor 2 (for example, an induction motor) having an output shaft 2a serving as a driving source, a motor pulley 10a fixed to the output shaft 2a of the motor 2, a motor speed detector 3 detecting a rotation speed of the motor 2, a belt 11 transmitting rotation force of the motor 2 to the rotor 1, a control unit 4 controlling the motor on the basis of an output from the motor speed detector 3, a motor drive unit 5 driving the motor 2 on the basis of an output from the control unit 4, and an operation panel 6 for inputting operation conditions such as a target rotation speed and an operation time of the rotor 1.
As shown in FIG. 12, the control unit 4 of the known belt-driven centrifuge 200 receives a target rotation speed setting value of the rotor 1 input from the operation panel 6 and an actual motor rotation speed detected by the motor speed detector 3 and calculates an application voltage V to the motor 2 and an excitation frequency f of the motor 2 on the basis of the target rotation speed setting value of the rotor 1 and the actual motor rotation speed, thereby controlling the motor 2.
In FIG. 12, the control unit 4 includes a target rotor rotation speed output unit 41 outputting a target rotation speed Nr* of the rotor 1 on the basis of the target rotation speed setting value of the rotor 1 input from the operation panel 6, a target motor rotation speed converting unit 45 converting the target rotation speed Nr* of the rotor 1 into the target rotation speed Nm* of the motor 2, a motor speed difference calculating unit 46 comparing the target motor rotation speed Nm* and the actual motor rotation speed Nm detected by the motor speed detector 3 so as to calculate the difference Ne, an application voltage calculating unit 47 calculating the application voltage V on the basis of the difference Ne and the actual motor rotation speed Nm, and an excitation frequency calculating unit 48 calculating the motor excitation frequency f on the basis of the actual motor rotation speed Nm.
More specifically, the target motor rotation speed converting unit 45 converts the target rotor rotation speed Nr* into the target motor rotation speed Nm* on the basis of an outer diameter ratio between the motor pulley 10a and the rotor pulley 10b. In other words, the target motor rotation speed Nm* is calculated on the basis of Equation 1.Nm*=Nr*×Dr/Dm  [Equation 1]
In Equation 1, Nm* represents a target motor rotation speed, Nr* represents a target rotor rotation speed, Dr represents an outer diameter of the rotor pulley 10b, and Dm represents an outer diameter of the motor pulley 10a. 
Then, the motor speed difference calculating unit 46 compares the target motor rotation speed Nm* and the actual motor rotation speed Nm so as to calculate the difference Ne (=Nm*−Nm), whereby the application voltage calculating unit 47 calculates the application voltage V to the motor 2 on the basis of the difference Ne and the motor rotation speed Nm using a well-known PID control (calculation) method. The excitation frequency calculating unit 48 calculates the motor excitation frequency f as a function of the motor rotation speed Nm on the basis of the motor rotation speed Nm. Therefore, the control unit 4 calculates the application voltage V and the excitation frequency f and controls the motor 2 only on the basis of the actual motor rotation speed Nm detected by the motor speed detector 3
Meanwhile, in the belt-driven centrifuge, it is known that slippage of the belt 11 occurs.